1. Field of the Invention
This invention relates to the art of vegetation control, and more particularly to a technique of a plurality of steps in the application of electromagnetic fields of two or more selected but different frequencies, in the sequence of at least one in the radio frequency range and the others in the microwave region, to the area in which vegetation is to be controlled.
2. Description of the Prior Art
The control of weeds has been recognized for centuries as necessary for maximum crop yield. If weeds are allowed to compete for water, soil nutrients, and space, there is generally a substantial drop in eventual crop income. Also, the weed population can contaminate a crop, e.g. red rice, and thus reduce the cash value of the crop. Prior to the 1940's, the only known method of weed control was laborious and expensive hand or mechanical weeding. In the late 1940's, the use of chemical herbicides began to dominate weed control activities. As the use of chemical herbicides escalated, many people began to show concern for the negative effects of the chemicals on the environment.
In 1978 U.S. Pat. No. 4,092,800 was issued. This patent taught the use of microwaves as a herbicide. This technique offered the advantage of control without leaving harmful residues or causing environmental pollution. The development of this method has generally been limited by the energy intensive requirements of this approach coupled with the high cost of fuel. Therefore, this technique has not achieved broad commercial development.
Thus, there has long been a need for an improved vegetation control method which is capable of utilizing electromagnetic waves at low cost.
Further, it is also desired that the method be useful under varying soil composition, compaction and condition.
Additionally, it is also desired that improved method of sterilizing the soil be provided to control fungi, nematodes, insects, etc. as well as weeds.